Electric power steering apparatus

Abstract

In an electric power steering apparatus, at least one of a speed reduction gear ratio of the speed reduction gear mechanism and the number of pole pairs of a motor resolver is set in such a manner that a calculated value, which is obtained by multiplying the speed reduction gear ratio of the speed reduction gear mechanism with the number of pole pairs of the motor resolver, represents a non-integer having a numerical value of the decimal place. This electric power steering apparatus includes an absolute rotational position specifying device configured to specify an absolute rotational position of the steering wheel from among plural possible absolute rotational positions that are obtained based on the steering angle and the motor electrical angle. This electric power steering apparatus is hence capable of controlling an electric motor based on the absolute rotational position of the steering wheel.

Description

FIELD OF THE INVENTION[0001]This invention relates to an electric power steering apparatus.BACKGROUND[0002]There is a conventionally known electric power steering apparatus, according to which an extent of a steering force needed for operating a steering wheel can be reduced by applying an assist force by a motor to a steering mechanism connected to a steering shaft. In this type of electric power steering apparatus, a steering wheel is rotated, within a limited rotational range, more than one turn (cf. one turn is 360 degrees) in a clockwise direction and more than one turn (cf. one turn is 360 degrees) in a counterclockwise direction. When a vehicle runs straight ahead, the steering wheel is defined to be positioned at a neutral steering position. A steering angle of the steering wheel is grasped by detecting, as an absolute steering position, a rotational position of the steering wheel on a basis of a degree of angle from this neutral steering position.[0003]The aforementioned st...

AI Technical Summary

Benefits of technology

The present invention relates to an electric power steering apparatus for vehicles. The apparatus includes a steering wheel, a steering shaft, a speed reduction gear mechanism, an electric motor, and a motor resolver for detecting the motor's electrical angle. The apparatus can control the electric motor to assist with steering the wheel. The invention also includes a rotational range restraining device for restraining the steering wheel within a predetermined range, and a memory for recording the wheel's position when the ignition switch is turned off. This allows for accurate positioning of the wheel and ensures proper operation of the vehicle. The invention also provides for different absolute rotational positions for the steering wheel within a limited range, which further enhances the accuracy of the wheel's position.

Problems solved by technology

In general, a steering wheel of a vehicle is not capable of controlling, only by its one turn (cf. one turn is 360 degrees) or less, an angle of a steered wheel within an entire steered angle.

For this reason, even where a mechanism such as “the steering angle sensor and the power steering device” disclosed in JP2002-145095A is employed, it is not possible to detect an absolute steering position of a steering wheel only by use of a single rotation angle sensor.

Meanwhile, a structure, in which the multiple number of rotation angle sensors are provided, however, directly results in an increase in a manufacturing cost, and a failure rate, of a power steering device, such that it appears to be a reality that this type of structure, which may cause an increase in the number of components, is not favorable to be employed.

However, it was found through researches of the present inventor that it may occur independent on some angular positions of the steering wheel that the latter known electric power steering apparatus cannot precisely distinguish some absolute rotational positions from others precisely or definitely.

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